Add --print-dependency-groups-to

Fixes fedora-python#81

README.rst

@@ -28,7 +28,15 @@ The ``tox-current-env`` plugin adds these options:
     This is useful for preparing the current environment for ``tox --current-env``.
     Use ``-`` for ``FILE`` to print to standard output.
 
-It is possible to use the two printing options together, as long as the ``FILE`` is different.
+``tox --print-dependency-groups-to=FILE``
+    Instead of running any ``commands``, simply prints the names of the
+    `declared dependency_groups <https://tox.wiki/en/latest/config.html#dependency_groups>`_
+    in ``dependency_groups`` to the specified ``FILE``.
+    This is useful for preparing the current environment for ``tox --current-env``.
+    Use ``-`` for ``FILE`` to print to standard output.
+    This option only exists with tox 4 and requires at least tox 4.22.
+
+It is possible to use the three printing options together, as long as the ``FILE`` is different.
 
 Invoking ``tox`` without any of the above options should behave as regular ``tox`` invocation without this plugin.
 Any deviation from this behavior is considered a bug.
@@ -93,7 +101,7 @@ Usage
 -----
 
 When the plugin is installed,
-use ``tox`` with ``--current-env``, ``--print-deps-to`` or ``--print-extras-to``
+use ``tox`` with ``--current-env``, ``--print-deps-to``, ``--print-extras-to`` or ``--print-dependency-groups-to``
 and all the other options as usual.
 Assuming your ``tox`` is installed on Python 3.7:
 
@@ -153,6 +161,20 @@ To get a list of names of extras, run:
      py37: commands succeeded
      congratulations :)
 
+To get a list of names of dependency groups, run:
+
+.. code-block:: console
+
+   $ tox -e py37 --print-dependency-groups-to -
+   py37 create: /home/pythonista/projects/holy-grail/tests/.tox/py37
+   py37 installed: ...you can see almost anything here...
+   py37 run-test-pre: PYTHONHASHSEED='3333333333'
+   group1
+   ...
+   ___________________________________ summary ____________________________________
+     py37: commands succeeded
+     congratulations :)
+
 
 Caveats, warnings and limitations
 ---------------------------------
@@ -167,6 +189,7 @@ The plugin is available also for tox 4. Differences in behavior between tox 3 an
 - The plugin does not check the requested Python version nor the environment name.
   If you let it run for multiple environments they'll all use the same Python.
 - Deprecated ``--print-deps-only`` option is no longer available.
+- The ``--print-dependency-groups-to`` is only defined on tox 4.
 
 Use an isolated environment
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/tox_current_env/hooks4.py

@@ -56,13 +56,23 @@ def tox_add_option(parser):
         help="Don't run tests, only print the  names of the required extras to the given file "
         + "(use `-` for stdout)",
     )
+    parser.add_argument(
+        "--print-dependency-groups-to",
+        "--print-dependency-groups-to-file",
+        action="store",
+        type=argparse.FileType("w"),
+        metavar="FILE",
+        default=False,
+        help="Don't run tests, only print the names of the required dependency-groups to the given file "
+        + "(use `-` for stdout)",
+    )
 
 
 @impl
 def tox_add_core_config(core_conf, state):
     opt = state.conf.options
 
-    if opt.current_env or opt.print_deps_to or opt.print_extras_to:
+    if opt.current_env or opt.print_deps_to or opt.print_extras_to or opt.print_dependency_groups_to:
         # We do not want to install the main package.
         # no_package is the same as skipsdist.
         loader = MemoryLoader(no_package=True)
@@ -72,14 +82,14 @@ def tox_add_core_config(core_conf, state):
         opt.default_runner = "current-env"
         return
 
-    if getattr(opt.print_deps_to, "name", object()) == getattr(
-        opt.print_extras_to, "name", object()
-    ):
+    exclusive = [getattr(getattr(opt, o), "name", object())
+                 for o in ("print_deps_to", "print_extras_to", "print_dependency_groups_to")]
+    if len(exclusive) != len(set(exclusive)):
         raise RuntimeError(
-            "The paths given to --print-deps-to and --print-extras-to cannot be identical."
+            "The paths given to --print-*-to options cannot be identical."
         )
 
-    if opt.print_deps_to or opt.print_extras_to:
+    if opt.print_deps_to or opt.print_extras_to or opt.print_dependency_groups_to:
         opt.default_runner = "print-env"
         return
 
@@ -98,9 +108,8 @@ def tox_add_env_config(env_conf, state):
     if opt.current_env:
         allow_external_cmds = MemoryLoader(allowlist_externals=["*"], pass_env=["*"])
         env_conf.loaders.insert(0, allow_external_cmds)
-    # For print-deps-to and print-extras-to, use empty
-    # list of commands so the tox does nothing.
-    if opt.print_deps_to or opt.print_extras_to:
+    # For print-*-to, use empty list of commands so that tox does nothing.
+    if opt.print_deps_to or opt.print_extras_to or opt.print_dependency_groups_to:
         empty_commands = MemoryLoader(commands=[], commands_pre=[], commands_post=[])
         env_conf.loaders.insert(0, empty_commands)
 
@@ -261,10 +270,21 @@ def prepend_env_var_path(self):
             )
             self.options.print_extras_to.flush()
 
+        if self.options.print_dependency_groups_to:
+            if "dependency_groups" not in self.conf:
+                raise RuntimeError(
+                    "tox is too old to know about dependency_groups."
+                )
+            print(
+                *self.conf["dependency_groups"],
+                sep="\n",
+                file=self.options.print_dependency_groups_to,
+            )
+            self.options.print_dependency_groups_to.flush()
+
         # https://github.com/fedora-python/tox-current-env/issues/75
         return super().prepend_env_var_path()
 
-
     @staticmethod
     def id():
         return "print-env"

tests/conftest.py

@@ -2,7 +2,7 @@
 import shutil
 
 import pytest
-from utils import FIXTURES_DIR, TOX4, modify_config, drop_unsupported_pythons
+from utils import FIXTURES_DIR, TOX_VERSION, TOX4, modify_config, drop_unsupported_pythons
 
 
 @pytest.fixture(autouse=True)
@@ -41,3 +41,16 @@ def print_deps_stdout_arg(request):
 def print_extras_stdout_arg(request):
     """Argument for printing extras to stdout"""
     return request.param
+
+
+@pytest.fixture
+def dependency_groups_support():
+    """Support for dependency groups"""
+    if (TOX_VERSION.major, TOX_VERSION.minor) < (4, 22):
+        raise pytest.skip(reason="requires tox 4.22 or higher")
+
+
+@pytest.fixture(params=("--print-dependency-groups-to-file=-", "--print-dependency-groups-to=-"))
+def print_dependency_groups_stdout_arg(request, dependency_groups_support):
+    """Argument for printing dependency groups to stdout"""
+    return request.param

tests/fixtures/pyproject.toml

@@ -1,3 +1,6 @@
 [build-system]
 requires = ["setuptools"]
 build-backend = "setuptools.build_meta"
+
+[dependency-groups]
+dg1 = ["build>=1"]

tests/fixtures/tox.ini

@@ -11,6 +11,8 @@ deps =
 extras =
     dev
     full
+dependency_groups =
+    dg1
 commands =
     python -c 'import os, sys; print(os.path.realpath(sys.exec_prefix), "is the exec_prefix")'
 # we explicitly clear this because the inner tox does not need to know